Composite foam for midsole

ABSTRACT

Embodiments herein relate generally to the field of footwear, and more particularly to components of performance footwear, such as midsoles, and in particular related to a high performance composite foam for a midsole, the composite foam comprising: a pelletized expanded thermoplastic elastomer; and a polyurethane (PU) matrix, wherein the pelletized expanded thermoplastic elastomer is mixed within the PU matrix. Midsoles made from a high performance composite foam and footwear including such midsoles. A method of making a high performance midsole is also provided.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the right of priority to and benefit of earlierfiling date of U.S. Provisional Application No. 62/658,161, filed onApr. 16, 2018, which is hereby incorporated herein by reference it itsentirety.

TECHNICAL FIELD

Embodiments herein relate generally to the field of footwear, and moreparticularly to foam for components of performance footwear, such asmidsoles.

BACKGROUND

Performance athletic footwear typically includes two primary components,an upper and a sole. The upper provides a covering for the foot andpositions the foot with respect to the sole. The sole is coupled to theupper and is generally configured to contact the ground during impact.In modern shoe design the sole provides cushioning during impact,traction, and motion control.

The structure of the sole portion of a performance athletic shoetypically has a layered configuration that may include an insole, aresilient midsole formed from a polymer foam material, and aground-contacting outsole that provides both abrasion-resistance andtraction. The midsole is the primary structural element that providescushioning and motion control. In many if not most performance athleticshoes, the midsole is made from a polymer foam. Polymer foams areparticularly suited for use in midsole construction because theircompression and resiliency attenuate reaction forces created by impactwith the ground. Conventional polymer foam materials are resilientlycompressible, in part, due to the inclusion of a plurality of open orclosed cells that define an inner volume substantially displaced by gas.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will be readily understood by the following detaileddescription in conjunction with the accompanying drawings. Embodimentsare illustrated by way of example and not by way of limitation in thefigures of the accompanying drawings.

FIG. 1 is a digital image of an exemplary composite foam for a midsole,in accordance with various embodiments.

FIG. 2 is a digital image of a toe to heel cross-sectional slice of anexemplary composite foam for a midsole, in accordance with variousembodiments.

FIG. 3 is a digital image of the exemplary composite foam of FIG. 2looking down (from the insole orientation), in accordance with variousembodiments.

FIG. 4 is a digital image of pelletized foam material used in acomposite foam, in accordance with various embodiments.

FIGS. 5A-5C are digital images showing the delamination/degranulation oftest foams not encompassed by this disclosure.

FIGS. 6A and 6B are digital images showing a midsole composed of acomposite foam, in accordance with various embodiments.

DETAILED DESCRIPTION OF DISCLOSED EMBODIMENTS

In the following detailed description, reference is made to theaccompanying drawings which form a part hereof, and in which are shownby way of illustration embodiments that may be practiced. It is to beunderstood that other embodiments may be utilized and structural orlogical changes may be made without departing from the scope. Therefore,the following detailed description is not to be taken in a limitingsense, and the scope of embodiments is defined by the appended claimsand their equivalents.

Various operations may be described as multiple discrete operations inturn, in a manner that may be helpful in understanding embodiments;however, the order of description should not be construed to imply thatthese operations are order dependent.

The description may use perspective-based descriptions such as up/down,back/front, and top/bottom. Such descriptions are merely used tofacilitate the discussion and are not intended to restrict theapplication of disclosed embodiments.

The terms “coupled” and “connected,” along with their derivatives, maybe used. It should be understood that these terms are not intended assynonyms for each other. Rather, in particular embodiments, “connected”may be used to indicate that two or more elements are in direct physicalcontact with each other. “Coupled” may mean that two or more elementsare in direct physical or electrical contact. However, “coupled” mayalso mean that two or more elements are not in direct contact with eachother, but yet still cooperate or interact with each other.

For the purposes of the description, a phrase in the form “A/B” or inthe form “A and/or B” means (A), (B), or (A and B). For the purposes ofthe description, a phrase in the form “at least one of A, B, and C”means (A), (B), (C), (A and B), (A and C), (B and C), or (A, B and C).For the purposes of the description, a phrase in the form “(A)B” means(B) or (AB) that is, A is an optional element.

The description may use the terms “embodiment” or “embodiments,” whichmay each refer to one or more of the same or different embodiments.Furthermore, the terms “comprising,” “including,” “having,” and thelike, as used with respect to embodiments, are synonymous.

Disclosed here is a composite foam for use in a midsole of performancefootwear. While certain embodiments are discussed with reference toperformance footwear such as shoes, embodiments herein may be applicableto a wide variety of activities, such as running and hiking; varioussports, such as volleyball, basketball, and tennis; various professions,such as medical, industrial, safety, rescue, and military, and othersuitable applications.

Foams used for midsole applications are expected to be lightweight,cushion, but rebound. Over time, the repeated compression-and-releasethat a midsole foam undergoes leads to ‘set’, meaning that it does notrebound as much as it did when it was new. It gets “set”, typically tosome increasing extent, in its compressed state. This is known in theindustry as ‘pack out’. It is desirable to have a midsole foam with highvalues of rebound, also known as resilience, and low values ofcompression set, while being lightweight.

The composite foam compositions disclosed herein include one or moreexpanded thermoplastic elastomers, such as an expanded thermoplasticpolyester elastomer (eTPEE), an expanded thermoplastic poly(ether-amide)(eTPEA) (e.g., a block copolymer with polyether and polyamide backboneblocks), an expanded thermoplastic polyolefin (eTPO), or an expandedblend of polymers in a pelletized form that is embedded within apolyurethane (PU) matrix (see, e.g. FIGS. 1-4 ). In embodiments, anexpanded thermoplastic elastomer includes one or more differentthermoplastic elastomers, such as described above.

Although the pellets are within the matrix, some of the pellet surfacesmay be visible on the exterior surface of a midsole made from suchfoams, see for example FIGS. 6A and 6B. One of the features that makescomposite foams so useful, is that the properties of both the expandedthermoplastic elastomer and PU can be tuned independently to create acomposite that exhibits a combination of properties that cannot beotherwise achieved, especially by blending the two materials whichgenerally leads to averaging of the physical properties, and a resultantcompromised product.

However, a major challenge in creating composites for applications inwhich the composite will be flexed or otherwise stressed is insufficientbonding at the interface between the two components, in this case theexpanded thermoplastic elastomer and NU interface. Because the twoprimary components of the disclosed composite foam are two differentpolymers there is an expectation that the interface would not be ofsufficient strength to resist delamination and/or degranulationresulting in mechanical failure at the interface, e.g. splitting. Thisexpectation was based in part on the finding that early composite foamscomposed of an expanded thermoplastic polyurethane (eTPU) and apolyurethane (PU) failed at the intermaterial interface (see e.g., FIGS.5A-5C). Thus, even though the components in the early composite foamswere both polyurethanes, the bonding at the interface was not goodenough to withstand flexing during wear tests. One of ordinary skill inthe art would not expect bonding to be improved by changing one of thecomponents to a different material type. More likely the expectationwould be that adhesives or surface modification protocols, with theadded cost and manufacturing step involved, would need to be considered.The expectation would have been that a composite of two linked materials(the expanded thermoplastic polyurethane pellets and the polyurethanematrix) would have had a significantly higher bond strength at theinterface than a pelletized expanded thermoplastic polyester or blockcopolymer elastomer and polyurethane matrix. Surprisingly however, whenevaluating alternative composite foam compositions, a composite of eTPEEand PU was found to have a significantly higher interface bond strengththan eTPU/PU composite (20 N/cm for the eTPEE/PU composite vs. 9 N/cmfor the eTPU/PU composite). While eTPU/PU hybrid composites can bemanufactured with better interfacial bond strength, they have not beenobserved to exhibit the overall combination of physical properties thatthe eTPEE/PU and eTPEE/PU hybrid composites exhibit.

Furthermore, this increase in interface bond strength was not made atthe expense of other desirable characteristics. As shown in Table 1below, the eTPEE/PU maintained desirable characteristics for aperformance foam, such as hardness, resilience and compression set whilehaving an increased wear resistance over the eTPU/PU composite, as shownby the split tear results.

TABLE 1 eTPU PIT eTPU/PU eTPEE/PU eTPEA/PU Hardness^(a) 40C 35C 45C 42C45C (Asker Scale) Density^(b) 0.22 0.31 0.30 0.30 0.19 (g/cm³) SplitTear^(c) >27 12.5 9 20 26 (N/cm) Resilience^(d) 55% 42% 53% 55% 64%Compression 45-50%   15% 51% 32% 33% Set^(e) ^(a)ASTM D-2240, SatraTM205-99 ^(b)Satra TM134-98 ^(c)Satra TM65 ^(d)ASTM D2632 ^(e)ASTM D395

With reference to Table 1, the eTPEE/PU and eTPEA/PU heterogeneouscomposites exhibit the best combination of high resiliency with lowcompression set. The high resiliency measured demonstrates a highrebound and high energy return, which are desired features for highperformance footwear. The low value for compression also demonstratesthe high durability of the composite foam. As previously described, thesplit tear strength is, for the heterogeneous composite materials, anindication of the interfacial bond strength, and how well the materialcan withstand flexing. The same wear trials that resulted in the poorinterfacial bonding exemplified by FIGS. 5A-5C have been successfullytried on footwear made from eTPEE/PU composite midsoles, resulting in nodelamination or degranulation failure. Similar results were observed forthe interface of the ePEA and PU. The eTPEE/PU hybrid exhibits higherenergy return than the PU, eTPU, and eTPU/PU hybrid materials. Thedynamic compression set for the eTPEE/PU hybrid is also lower than thedynamic compression set for the eTPU and eTPU/PU hybrid materials. Lowerdensity hybrid composites can be made using Pebax® (Arkema), apoly(ether amide), without significantly compromising the energy return.While the PU exhibits lower dynamic compression set (3%), it alsoexhibits lower energy return. By combining the PU and eTPEE to make ahybrid composite, a cushioning material can be made with high energyreturn and low compression set.

The disclosed composite foam composition includes an expandedthermoplastic elastomer in a pelletized form embedded within apolyurethane (PU) matrix, such as eTPEE, eTPEA, eTPO, or an expandedblend of polymers. In embodiments, the expanded thermoplastic elastomerpellets are generally spheroid in shape with major and minor axesranging between about 1 mm to about 12 mm, such as about 2 mm to about 8mm. In embodiments, the expanded thermoplastic elastomer pellets have adensity of between about 0.06 g/cm³ and about 0.20 g/cm³, such as about0.11 g/cm³ or 0.13 g/cm³. This low density combined with otherproperties, such as a resilience of greater than about 50% or 60%,provides a foam material useful as a midsole for performance footwear.

In an example, the disclosed composite foam composition includes anexpanded thermoplastic polyester elastomer (eTPEE) in a pelletized formembedded within a polyurethane (PU) matrix. In embodiments, the eTPEEpellets are generally spheroid in shape with major and minor axesranging between about 1 mm to about 12 mm, such as about 2 mm to about 8mm. In embodiments, the eTPEE pellets have a density of between about0.08 g/cm³ and about 0.20 g/cm³, such as about 0.13 g/cm³. This lowdensity combined with other properties, such as a resilience of greaterthan about 50%, provides a foam material useful as a midsole forperformance footwear.

In an example, disclosed composite foam composition includes an expandedthermoplastic poly(ether amide) (eTPEA) in a pelletized form embeddedwithin a polyurethane (PU) matrix. In embodiments, the eTPEA pellets aregenerally spheroid in shape with major and minor axes ranging betweenabout 1 mm to about 12 mm, such as about 2 mm to about 8 mm. Inembodiments, the eTPEA pellets have a density of between about 0.08g/cm³ and about 0.20 g/cm³, such as about 0.11 g/cm³. This low densitycombined with other properties, such as a resilience of greater thanabout 60%, provides a foam material useful as a midsole for performancefootwear.

In another example, disclosed composite foam composition includes anexpanded thermoplastic polyolefin (eTPO) in a pelletized form embeddedwithin a polyurethane (PU) matrix. In embodiments, the eTPO pellets aregenerally spheroid in shape with major and minor axes ranging betweenabout 1 mm to about 12 mm, such as about 2 mm to about 8 mm. Inembodiments, the eTPO pellets have a density of between about 0.08 g/cm³and about 0.20 g/cm³. This low density combined with other properties,such as a resilience of greater than about 60%, provides a foam materialuseful as a midsole for performance footwear.

In an example, disclosed composite foam composition includes a blend ofpolymers, e.g., an expanded blend of polymers in a pelletized formembedded within a polyurethane (PU) matrix. In embodiments, the pelletsare generally spheroid in shape with major and minor axes rangingbetween about 1 mm to about 12 mm, such as about 2 mm to about 8 mm. Inembodiments, the pellets have a density of between about 0.08 g/cm³ andabout 0.20 g/cm³. This low density combined with other properties, suchas a resilience of greater than about 60%, provides a foam materialuseful as a midsole for performance footwear.

In an embodiment, the composite foam is prepared by mixing the expandedthermoplastic elastomer pellets with a polyisocyanate and a polyolprepolymer containing chain extender, water, pigment, stabilizers, andother additives, to form a slurry. The mixing ratio of polyisocyanate topolyol prepolymer is in the range of 0.5 to 1.5, depending on specificchemical structure of each component and the processing conditions. Inanother embodiment, the composite foam is prepared by mixing theexpanded thermoplastic elastomer pellets with a single-componentpolyurethane prepolymer containing blowing agent, pigment, stabilizers,and other additives, to form a slurry. The weight percentage of expandedthermoplastic elastomer pellets to PU is 40% to 70%. The mixing occursat 40 to 50° C., and the slurry is then poured into a mold for PUexpansion and curing. The top plate of the mold is closed, and then theexpansion and curing occurs over the course of 5 to 20 minutes, abouthalf of which time the mold is 60 to 80° C. In some manufacturingprocess set-ups, the expansion and curing time may be shortened by usingmolds that allow more efficient heat maintenance and transfer

In embodiments, a formed midsole made from a disclosed composite foamhas a density of about 0.10 g/cm³ to about 0.40 g/cm³, such as about 0.2g/cm³ or 0.3 g/cm³. In embodiments, a formed midsole made from adisclosed composite foam has an Asker hardness of at least 35 C, forexample greater than about 40 C, such as between about 40 C and about 55C, e.g. about 42 C. In embodiments, a formed midsole made from adisclosed composite foam has a split tear value of at least 15 N/cm, forexample at least 16, 17, 18, 19, 20, 25, 30 and 35 N/cm, such as betweenabout 18 and about 28 N/cm, e.g., about 20 N/cm or 26 N/cm. Inembodiments, a formed midsole made from a disclosed composite foam has aresilience of at least about 40%, such as at least 45%, at least 46%, atleast 47%, at least 48%, at least 49%, or at least 50%, for examplebetween about 50% and 70%, such as about 55%, 64%, or 68%. Inembodiments, a formed midsole made from a disclosed composite foam has adynamic compression set below about 12%, such as below about 11%, 10%,9%, 8%, or even 7%.

FIGS. 1-3 are digital images of composite foams, in accordance withvarious embodiments. FIG. 1 is a digital image of an exemplary compositefoam 10 for a midsole, in accordance with various embodiments. FIG. 2 isa digital image of a toe to heel cross-sectional slice of an exemplarycomposite foam 10 for a midsole, in accordance with various embodiments.FIG. 3 is a digital image of the exemplary composite foam 10 of FIG. 2looking down (from the insole orientation), in accordance with variousembodiments. With reference to FIGS. 1-3 , the composite foam 10 iscomposed of expanded thermoplastic elastomer pellets 12 (eTPEE pelletsin this example) homogenously mixed (mixed throughout in a substantiallyuniform distribution) within a PU matrix 14. FIG. 4 is a close up of theexpanded thermoplastic elastomer pellets 12 prior to mixing with the PU.FIGS. 6A and 6B are digital images showing a midsole 20 composed of acomposite foam 10, in accordance with various embodiments.

Example 1

Slabs of eTPU/PU and eTPEE/PU hybrid composites were prepared at thesame 60/40 weight percentages of expanded pellets to PU resin. Slabs ofeTPEA/PU hybrid composites were prepared at a 50/50 weight percentage.Data were collected and are shown in the table below.

Density Energy Dynamic (g/cm³) Return^(a) Compression Set^(b) PU 0.3057% 3% eTPU 0.24 57% 10%  eTPU/PU 0.19 56% 12%  eTPEE/PU 0.29 65% 7%eTPEA/PU 0.20 62% 7% ^(a)ASTM F1976 ^(b)Measured after 100,000degradation cycles, simulating a 100-mile run based on an average stridelength of a male runner.

Data are averages of two measurements. Dynamic compression set measuredafter 100,000 degradation cycles (5 J), simulating a 100-mile run basedon an average stride length of a male runner, using a custom-builtdegradation machine. Samples were slabs molded to be between 18 and 26mm thick. After 100,000 cycles, slabs were allowed to recover for 1 hourand then the thickness measured. The difference between this measuredthickness and the original thickness were used to compute the dynamiccompression set. Energy return was measured in an impact device.

The eTPEE/PU and eTPEA/PU hybrid composites exhibit higher energy returnthan the PU, eTPU, and eTPU/PU hybrid materials. The dynamic compressionset for the eTPEE/PU and eTPEA/PU hybrids is also lower than the dynamiccompression set for the eTPU and eTPU/PU hybrid materials. Lower densityhybrid composites can be made using expanded poly(ether amide) pellets,without significantly compromising the energy return. While the PUexhibits lower dynamic compression set (3%), it also exhibits lowerenergy return. By combining the PU and expanded thermoplastic elastomerto make a hybrid composite, a cushioning material can be made with highenergy return and low compression set.

Although certain embodiments have been illustrated and described herein,it will be appreciated by those of ordinary skill in the art that a widevariety of alternate and/or equivalent embodiments or implementationscalculated to achieve the same purposes may be substituted for theembodiments shown and described without departing from the scope. Thosewith skill in the art will readily appreciate that embodiments may beimplemented in a very wide variety of ways. This application is intendedto cover any adaptations or variations of the embodiments discussedherein. Therefore, it is manifestly intended that embodiments be limitedonly by the claims and the equivalents thereof.

What is claimed is:
 1. A high performance composite foam for a midsolecomprising: a pelletized expanded thermoplastic elastomer comprising anexpanded thermoplastic polyester elastomer; and a polyurethane (PU)matrix, wherein the pelletized expanded thermoplastic elastomer is mixedwithin the PU matrix.
 2. The high performance composite foam of claim 1,wherein the pelletized expanded thermoplastic elastomer comprises anexpanded thermoplastic poly(ether amide) elastomer.
 3. The highperformance composite foam of claim 1, wherein the pelletized expandedthermoplastic elastomer comprises an expanded thermoplastic polyolefin.4. The high performance composite foam of claim 1, wherein thepelletized expanded thermoplastic elastomer comprises an expanded blendof thermoplastic polymers.
 5. The high performance composite foam ofclaim 1, wherein the pelletized expanded thermoplastic elastomer isspheroid in shape with major and minor axes ranging between about 1 mmto about 12 mm.
 6. The high performance composite foam of claim 1,wherein the pelletized expanded thermoplastic elastomer pellets have adensity of between about 0.06 g/cm³ and about 0.20 g/cm³.
 7. The highperformance composite foam of claim 1, wherein the PU matrix is preparedfrom one or more polyisocyanates and one or more polyols.
 8. The highperformance composite foam of claim 1, wherein the composite foam has adensity of about 0.18 g/cm³ to about 0.40 g/cm³.
 9. The high performancecomposite foam of claim 1, wherein the composite foam has an Askerhardness at least 35 C.
 10. The high performance composite foam of claim1, wherein the composite foam has a split tear value of at least 15N/cm.
 11. The high performance composite foam of claim 1, wherein thecomposite foam has a resilience of at least about 40%.
 12. The highperformance composite foam of claim 1, wherein the composite foam hasdynamic compression set below about 12%.
 13. The high performancecomposite foam of claim 1, wherein the expanded thermoplastic elastomeris mixed homogenously within the PU matrix.
 14. A midsole for footwearcomprising the high performance composite foam of claim
 1. 15. Anarticle of footwear comprising the midsole of claim
 14. 16. A method ofmaking a high performance midsole comprising: mixing a pelletizedexpanded thermoplastic elastomer and a polyurethane (PU) matrix, thepelletized expanded thermoplastic elastomer comprising an expandedthermoplastic polyester elastomer; and molding the expandedthermoplastic elastomer PU mixture to form the midsole.
 17. The methodof claim 16, wherein the pelletized expanded thermoplastic elastomercomprises an expanded thermoplastic poly(ether amide) elastomer.
 18. Themethod of claim 16, wherein the pelletized expanded thermoplasticelastomer comprises an expanded thermoplastic polyolefin.
 19. The methodof claim 16, wherein the pelletized expanded thermoplastic elastomercomprises an expanded blend of thermoplastic polymers.
 20. The method ofclaim 16, wherein the pelletized expanded thermoplastic elastomer isspheroid in shape with major and minor axes ranging between about 1 mmto about 12 mm.
 21. The method of claim 16, further comprising preparingthe PU matrix from one or more polyisocyanates and one or more polyols.22. The method of claim 16, further comprising forming the pelletizedexpanded thermoplastic elastomer.